This invention relates to food preservation apparatus for canning, and in particular to a closely controlled and monitored temperature and pressure cooking unit suitable for home canning or for canning on an intermediate scale where portability of the equipment is advantageous. Because of the very serious consequences in improperly processed food, reliability in both the process and the apparatus is necessary for confident consumption of the food preserved. Key to this cooking unit is a unique low pressure regulator for controlling the gas flow to a heating burner which is operated in conjunction with a pressure cooker or retort. The pressure regulator comprises a sensitive flow control valve monitored by the steam pressure within the retort in a closed loop operation that accurately maintains a preselected temperature within the retort. The temperature within the retort is continuously recorded by a thermal recording device and accurately verified by a triple or single element thermometer tree in order that the canning process can be fully monitored.
Historically, canning was a long sought answer to the problem of food preservation, which became particularly acute during times of war in providing armies with the necessary food supplies. Nicolas Appert, a Frenchman is credited with discovering the method of food preservation by heating prepared food and hermetically sealing the food in sterilized containers. By trial and error he established various temperatures and durations for different foods. In the subsequently developed canning with tin cans, as opposed to glass jars, the cans are usually filled and sealed before the sealed cans are heated to the prescribed temperatures for the required duration.
Since spoilage of food is caused by enzyme activity or the growth of microorganisms such as bacteria, molds or yeast, destruction of such by application of heat will prevent spoilage if the food is subsequently isolated from reinfestation by sealing the food in containers. Because the temperature and duration of heating affects the composition and consistency of the food, as well as the nutritional value of the food, it is desirable that the minimum temperature and duration be applied to prevent overcooking of the food. For nonacid foods, in order to assure destruction of the spores of clostridium botulinum, which can generate a deadly poison, the food must be heated at the boiling point for more than five hours. However, by raising the temperature above the boiling point to 240.degree. or 250.degree. F., the duration of heating can be substantially reduced. A pressure cooker is thereby necessary to allow for use of higher than boiling point temperatures to optimize the temperature and duration of cooking to insure proper preservation and maximum quality of the food preserved.
The canning unit devised is designed to insure both the quality of the food and sufficiently of the preserving process on less than a large commercial scale canning endeavor.